This invention relates to a control circuit for a multi-product dispenser. A multi-product dispenser (referred to in this application as a "MPD,") is a fuel dispenser which includes in a single cabinet provisions for dispensing several grades or types of fuel. The cabinet, typically positioned on an island at a service station or convenience store, may have control circuitry and valving which permits one of several grades of fuel, for example, regular, mid-grade and premium grades of gasoline motor fuel, to be selectively dispensed through a single dispensing nozzle, or from a selected one of several nozzles connected to respective fuel supplies. The electrical circuits which control these dispensers are subject to regulations by several organizations. For example, National Electrical Code ("NEC") and National Fire Prevention Association ("NFPA") regulations require that "each circuit leading to or through dispensing equipment shall be provided with a switch or other acceptable means . . . to disconnect simultaneously from the source of supply all conductors of the circuit, including the grounded conductor, if any." NEC and NFPA 30A, Section 514-5. Sections (b) and (c) of NEC 514-5 and the notes to NFPA 30A further require emergency shutdown capability so that all electric power to the dispenser may be interrupted. NEC Section 514-6, new in 1999, further requires that "each dispensing device shall be provided with a means to remove all external voltage sources, including feedback, during periods of maintenance and service of the equipment."
The invention of this application is intended specifically to meet all of the current electrical and fire code requirements relevant to MPDs, and to do so by means of a single modular circuit board.
Conventional control circuits require that many of the circuit components be mounted and wires run between them in the field. Many such components must be mounted in their own electrical enclosures connected by conduits or raceways, or combined into a single enclosure unit by the field electrician. Thus, physical layout and groupings of components can differ from installer to installer based upon individual preferences. This variability can result in miswiring and consequent damage to equipment, overheating, construction delays and excessive repair costs. Even when all of the wiring is done correctly during installation, the variability in wiring may result in incorrect repairs or maintenance, particularly when carried out by different personnel than those who carried out the initial installation.
U.S. Pat. No. 4,719,532 ("'532 Patent") describes an electrical controller for actuating a number of electrical devices according to control inputs received from a number of control input sources, specifically including a number of optical isolators which function to electrically isolate each of the control input sources from each other. The controller described in the '532 Patent does not provide a means to simultaneously disconnect from the supply all conductors of each dispenser circuit, as required by NEC and NFPA 30A, Section 514-5.
The controller described in the '532 Patent provides for emergency shutdown of the fuel pumps which deliver fuel to the MPD, but does not provide a means for interrupting power to the dispenser itself, as required by Sections (b) and (c) of NEC 514-5 and NFPA 30A.
The controller described in the "532 Patent provides a means of removing external voltage feedback from the dispenser during maintenance and repair, but does not provide a means of disconnecting the power feed to the dispenser. Rather, the device of the '532 Patent addresses voltage isolation only on the downstream side of the fueling dispenser, but does not have means to control power fed upstream to the dispenser, including lighting.
The controller described in the '532 Patent also limits the number of dispensers that can be connected based upon the number of input connections provided and the particular configuration of the matrix switch used. Thus, any expansion plans are required to be considered at the time of initial installation. Misjudgments may result in either too little or too much capacity.
Finally, the controller described in the '532 Patent is designed in such a manner that all the inputs and outputs must be disconnected while the unit is being replaced or repaired.